I save whenever and wherever I can. I have had CTD's occasionally but I wouldnt say Im plagued with them.
Just save often and under different conditions. For example you get a contact report make sure you are surfaced and save. Then when you close in.. save again... I usually dive to periscope depth and save again when Im in shooting distance. My patrols have had up to 8 or 9 saves a piece.
GL